There is conventionally known, as an image forming apparatus, a printer in which a cartridge having a developing roller is detachably mountable.
As such a printer, there is proposed a printer including a developing device provided with a gear train for a drive system, and a side cover for protecting the gear train.
Such a printer further includes a toner replenishing member for replenishing the developing device with toner. The developing device and the toner replenishing member are detachably attached to a main casing of the printer.